ABSTRACT

A molecular ecological study was performed on an Australian soil sample to unravel a substantial portion of the bacterial diversity. A large fragment of the 16S rRNA gene was amplified, using DNA isolated by lysing the microorganisms directly within the soil matrix, and a clone library was generated. Comparative sequence analysis of 30 clones and dot blot hybridization of 83 additional clones with defined oligonucleotide probes revealed the presence of three major groups of prokaryotes of the domain Bacteria. The first one comprises 57 clones that indicate relatives of nitrogen-fixing bacteria of the alpha-2 subclass of the class Proteobacteria; the second group of 7 clones originates from members of the order Planctomycetales that, however, reveal no close relationship to any of the described Planctomycetales species; 22 clones of the third group are indicative of members of a novel main line of descent, sharing a common ancestry with members of planctomycetes and chlamydiae.